The invention pertains to the field of data storage systems, and more particularly to point-in-time copying operations in data storage systems.
It is known to perform so-called ‘point-in-time’ copying of data in data storage systems for a variety of purposes, including data backup, data mining/analysis, etc. In a point-in-time copying operation, a source storage volume as it exists at the beginning of the operation is copied to a target volume. Upon completion, the target volume contains an exact copy of the source volume as existing at the time the copy operation was initiated. Various known mechanisms may be used to handle ongoing data reads and writes while the copying operation is in progress.
In data processing systems employing so-called “mainframe” host computers, such as zSeries® servers sold by IBM Corporation, a particular point-in-time copying utility known as Flashcopy® may be utilized. Flashcopy provides a point-in-time copy of a logical volume (in whole or in part) with almost instant availability of both the source and target volumes for continuing data accesses. The Flashcopy operation includes an “establish” phase in which a Flashcopy relationship is established between source and target volumes, followed by a “copy” phase in which the data is copied from source to target volume. By default, copying occurs in the background such that normal I/O processing can continue. The Flashcopy relationship is automatically terminated once all source volume tracks have been copied to the target volume, unless an option referred to as “persistent Flashcopy” is utilized, in which case the relationship must be explicitly ended or withdrawn by an application program. The Flashcopy functionality is carried out primarily by a controller in response to Flashcopy I/O commands issued by an application program in the host computer.
An alternative point-in-time data copying utility known by the name SNAP is sold by EMC Corporation. SNAP is supported on EMC's SYMMETRIX® storage systems. Beyond the firmware support within the SYMMETRIX systems, SNAP relies on an application program interface (API) that is incorporated into a host computer. SNAP functions are invoked via the SNAP API, which communicates with the SNAP firmware within the SYMMETRIX to carry out the functions. SNAP is largely a superset of Flashcopy, i.e., SNAP includes the main features of Flashcopy as well as additional features not included in Flashcopy. Among other things, SNAP has the capability of performing point-in-time copying of volumes that are mirrored utilizing Symmetrix Remote Data Facility (SRDF) also sold by EMC Corporation. Although Flashcopy has analogous functionality, it is limited to use with a proprietary remote copying technique known as Peer-to-Peer Remote Copy (PPRC) and does not support SRDF for example. Flashcopy also has other limitations not present in SNAP.